Field of the Invention
The present invention relates generally to an optical apparatus and an image pickup apparatus, and more particularly to an optical apparatus and an image pickup apparatus having the same, each of which can obtain polarization information.
Description of the Related Art
One conventional image pickup apparatus can highlight and detect a predetermined feature of an object by observing a polarization state of light from the object. For example, a polarization filter attached to a front surface of a lens in a single-lens reflex camera in imaging an object can highlight the quality or feel of the object, such as a color and a contrast, or highlight or reduce the glare of reflected light on a water surface, etc. An inspection apparatus etc. is also known which can detect an edge or defect of the object.
Stray light, such as ghost and flare, may appear in a captured image due to an illumination state of an object, an image pickup condition of an optical system, etc. The stray light not only deteriorates the quality of the image but also is recorded as information (an error) different from the object information when the polarization information of the object is obtained. In particular, due to the multiple reflections on an image display device surface in an image display device and on the optical plane in an optical system in an image pickup system, the polarization depends on an incident angle and thus it is difficult to distinguish the polarization information of the object from the polarization information of the stray light. As a solution for this problem, Japanese Patent No. 5,045,504 discloses a method for utilizing a difference of a polarization reflectance in an antireflection film in the optical system to reduce the stray light through a polarizer.
However, the method disclosed in Japanese Patent No. 5,045,504 cannot distinguish the object and the stray light from each other where a polarizer is used to obtain the polarization information. Moreover, this method cannot effectively reduce concurrent stray light fluxes at different angles of view in the image, and stray light with a small incident angle on an optical plane in an image pickup lens system, such as stray light reflected between an image pickup element and an optical system.